Ales brooking davis



Patented Feb. 26, 1 929.

UNl'lED STATES ALEX BROOKING DAVIS, OF CINCINNATI, OHIO, ASSIGNOR TO THE KEYSTONE "\VAT Parent cl rics.

CASE 00., OF RIVERSIDE, NEW JERSEY, A CORPORATION OF PENNSYLVANIfi.

PROCESS OF PHOTOGRAPHIC ETCHING AND LIGHT-SENSITIVE RESIST.

No Drawing. Original application filed October 30, 1926, Serial No. 145,373. Divided and this application filed November 15, 1928. Serial No. 319,742.

This invention pertains to the art of photo October 30, 1926, for improvements in process of photographic etching and light sensitive resist therefor.

One of the well known ways of producing etchings is to apply a light sensitive composition or film to a surface, and subject the film to light with a screen carrying a design interposed. The design carried by the screen then becomes photographed in the film. This film is then subjected to a developer which functions to remove certain portions of the. film from the surface. This surface is then subjected to an etching solution which attacks to any desired extent, the surface which is not covered by portions of the film. After the etching operation the portions of the film which remained on the surface are removed in any known manner.

It is well understood in the art of photographic etching that the action of the light on the film renders insoluble the portions of the film which are subjected to the light and it is those portions which are not removed by the developer.

)ne of the objects of this invention is to produce an improved process of photographic etching and to furnish a novel and improved light sensitive composition which is highly satisfactory for use in process.

A further object of the invention is the provision of a satisfactory process by which I a design may be reproduced clearly and in a sharply defined manner, and to provide a highly light sensitive film or coating for use as a resist in an etching process.

Another object of this invention is the provision of new compositions of materials, each constituent of which may be more or less light sensitive but the combination of which produces a materially light sensitive composition which is particularly adaptable as a photographic resist.

A still further object is the provision of a satisfactory water soluble resist which is suitable for photo etching have been developed, and these fall in two distinct groups; those which are soluble in water at the outsetaud which are applied in the form of their aqueous solutions, and those which are insoluble in water but soluble in organic solvents and which are applied in the form of their solution in organic solvents, the film being deposited in a solid state by evaporation of the solvent. 'Bichromate gelatine combinations are representative of the first class above mentioned, and asphalt, certain metallic resinates and certain gelatinized drying oils are representative of the latter class.

The invention relates particularly to improvements in the class of water soluble combinations and more especially to the character of organic sensitizers which may be combined with proteins such as gelatine or glue.

While the proteins such as glue or gelatine are generally slightly light sensitive, it has been found from experience that certain other materials which of themselves are light sen sitive to a degree, may be added to the proteins to thereby form a most satisfactory photographic film and resist. Numerous experi- I ments which have been made show that of the many readily obtainable highly active organic sensitizing agents, there are a few which combine with the gelatine or glue in a satisfactory form so as to produce a highly efficient photographic film. The preferred organic sensitizing agents fall within the group of mono-hydroxy aldehydes and include the aliphatic mono-hydroXy aldehydes. It has been found that aldol which comes within this classification is particularly advantageous to be combined with a protein and a bichromate to form a most satisfactory photographic film for etching purposes. AL dol possesses an aldehyde group and is chemically beta-hydroxy-butyric aldehyde. It is condenser attachment for concentrating the miscible with Water and alcol'rol in all proportions and boils at 83 C. under 20 mms. and When pure is a thick syrupy substance. Aldol under the action of light changes its condition due to more or less polymerization. It also reacts under the action of light with many organic substances, and particularly those bearing an amino group such as aniline, toluidine aand bnapl ithylaminc- Al dol also is particularly responsive to. light When combined with proteins and protein degradation products;

Experiments have shown that'whi l 'e a'ldol alone acts with proteins under the action of light, also do the alkali bichromates, it has been found that when both are used in combination at the same time each seems to accelerate the action of the other. Thus a bi'chromate glue mixture to 'WlllCl'I aldol has been added is much more active than the bichromate glue alone, and an aldol gelati'ne combination is rendered insoluble under the action of light at a' far more rapid rate when alkali lai'chromatesv have been added to it,

. and it is this fact that forms an important part of this invention. llt'hasalsobeen found that compositions of thematerials above noted give a much better etching result and the l ines of the design are more sharply defined and the resist does not tend to scale off.

As an illustration oat. the advantage of the addition of ald'o'l I have found that a bichrom'ate gl ue preparation of certain definite proportions becomes insolublein Water'und'cr the action of light in two and one-half minutes, While if a small amount oli al' dol be added to this same'mass, it then becomes insoluble under the action of light in twenty seconds, and I have obtained good resists from films-Which had been exposed only seven seconds.

As a specific example of how the invention may be: carried out,-the following Willv serve:

Nine parts of photoengravers liquid. glue are mixed with five parts of solution of ammonimn bichromate' of tWen't 1 per cent strength by weight. The metal. part to be etched or decorated: is now coated: in: any suitable manner with this solution and the excess removed. by centrifugal force as on. a

spinning machine or any other suitable mannet. The entire deposited coat of blClll'O- mate glue is now moistened over the surface with pure a-ld ol and the excess immediately removed. 11f the parts to be treated are small, the whole operation may be carried out on. a spinning 1nach:ine,-tlrc bichromate glue solution being poured upon] the excess spun off and the aldol' ly applied to the resulting su mediately that the ex. ess al'dol has been removed, the surface is ready for can light any known mam. er, such as ot-the usual arc projection machincswith a mediateriz e.

1e surface,

light areas and; designs'are obtained uponthe coated surface by means of an interposed picture Wnich may be either a negative or a positive. Exposure for thirty seconds with the composit on ab ve ment oned s si'i'l'licient to render the res 7 insoluble,

(:3 V be employed to coat the (lGSl-lfl'i i with the mixture of bicbromate: i

one and: to

then apply th small amoum or all 01.. It W'l-ll aiso be understood that the hichrt ziated glue and the aldol may be mixed together before they are placed on. the surface and. in that case it is desirable to coat/the suriiace Wi a short time and. to expose the same to toe proj ecting light without delay. While it has been described that one form 0% actfinin'g the resist to the sin-face after develop ment is by means of the baking step in the process, it Will be understood that other operationsmay be employed to accomplish this end. i

Itis believed that a reaction takes placebotween the mixture of the glue and. bichromate andthe a;ld.o:l1,and that a compound solution is formed therefrom giving a single filnr.

It will be understood that from: the: above described composition 01: compound or film and process that the exact composition of the glue or its source may be varied mateto alidol; which are active in similar manner andwhich give entirely satisfactory effects. Theinvention herein is, therefore, regarded as including the use of any aliphatic monohydroxy aldehyde in combination with an alkali bichromate and a portein.

t Will: also be; seen that the simple composition of the film or resist, and the process of the ctcl and the very quick time in which the inn 5 V in the film or resist all cooperate to increase the ediciency of the etching process and to thereby permit quick and satisfactory etchhot plate or and the picture '13 developed by simply Wash-mg out the tration of the etcn methods may e or picture may be produced ing which may be accomplished Within a commercial cost. Many advantages and uses of this process and the novel resist may readily suggest themselves, and it is to be understood that such advantages and uses are to be considered as being Within the scope of the invention herein defined. Also the modification of the amounts of the materials of the composition may be made. Likewise such modifications are considered as being Within the scope of this invention as herein set forth in the claims.

VVh-at is claimed is:

1. A resist for photographic etching comprising a protein, an alkali bichromate, and a hydroXy butyric aldehyde.

2. A resist for photographic etching comprising a compound bearing an amino group, a bichromate, and a hydroxy butyric alde hyde.

3. A resist for photographic etching comprising animal glue, ammonium bichromate and a hydroxy butyric aldehyde.

4. A resist for photographic etchingcomprising animal glue, ammonium hichromate, and aldol.

5. A resist for photographic etching comprising gclatine having ammonium bichromate incorporated therein, and aldol.

6. A photographic etching film composed of a protein, an alkali bichromate and aldol, and having a design photographed therein.

7. In the process of photographic etching, the step which consists in depositing upon a surface of an article to be etched a film including a protein, an alkali bichromate, and an aliphatic mono-hydroxy aldehyde.

8. A resist for photographic etching comprising a protein, an alkali bichromate, and a mono-hydroxy-aldehyde.

9. A resist for photographic etching comprising a compound bearing an amino group, a bichromate, and a mono-hydroxy-aldehyde.

10. A resist for photographic etching comprising animal glue, ammonium bichromate and mono-hydroxyaldehyde.

ALEX BROOKING DAVIS. 

